In many houses, television and/or video signals are received through cable or satellite links at a set-top box at a fixed point in the house. In many cases, it is desired to place a screen at a point a distance from the set-top box by a few meters. This trend is becoming more common as flat-screen using plasma or liquid crystal display (LCD) televisions are hung on a wall. Connection of the screen to the set-top box through cables is generally undesired for aesthetic reasons and/or installation convenience. Thus, wireless transmission of the video signals from the set-top box to the screen is preferred. Similarly, it may be desired to place a computer, game controller, VCR, DVD, or other video source that generates images to be displayed on a screen a distance from the screen.
Generally, the data are received at the set-top box compressed in accordance, for example, with the motion picture expert group (MPEG) format and are decompressed by the set-top box to a high quality raw video signal. The raw video signal may be in an analog format or a digital format, such as the digital video interface (DVI) format or the high definition multimedia interface (HDMI) format. These digital formats generally have a high definition television (HDTV) data rate of up to about 1.5 Giga bits per second (Gbps).
Wireless short range transmission in the home can be done over the unlicensed bands around 2.4 GHz or around 5 GHz (e.g., in the U.S 5.15-5.85 GHz band). These bands are currently used by wireless local area networks (WLAN) where the 802.11 WiFi standard allow maximal data rates of 11 Mbps (802.11b), or 54 Mbps (for 20 MHz bandwidth and the 802.11g/802.11a standards). Using the emerging Multi-Input Multi-Output technology the data rate of the emerging 802.11n standard can increase to above 200 Mbps when a 20 MHz band is used and double of that when a 40 MHz band is used. Another alternative is to use Ultra Wide Band (UWB), which claims to provide 100-400 Mbps.
Since the available data rate is lower than the 1.5 Gbps needed for uncompressed HDTV video, the video generally needs to be recompressed for wireless transmission, when desired. Known strong video compression methods, e.g. those having a compression factor of above 1:30 require very complex hardware to implement the compression. This is generally not practical for home applications. These compression methods generally transform the image into a different domain by using, for example, wavelet, discrete cosine transform (DCT), or Fourier transforms, and then perform the compression in that domain. The transforms typically de-correlate the data to allow for effective compression. In PCT application IL/2004/000779, Wireless Transmission of High Quality Video, assigned to common assignee and incorporated herein in its entirety by this reference thereto, there is shown a method of transmitting video images. The method includes providing high definition video, compressing the video using an image domain compression method, in which each pixel is coded based on a vicinity of the pixel, and transmitting the compressed video over a fading transmission channel.
In U.S. patent publication 2003/002582 to Obrador there is described a wireless transmission of images which are encoded using joint source channel coding (JSCC). The transmitted images are decomposed into a plurality of sub-bands of different frequencies. Image and corresponding boundary coefficients with a lowest resolution are sent first and then image and boundary coefficients with a higher resolution are transmitted. An exemplary JSCC applies channel encoding techniques to the source coded coefficients, providing more protection to more important, i.e. low frequency, coefficients and less protection to less important, i.e. high frequency, coefficients. Another technique for JSCC was proposed by Ramstad, The Marriage of Subband Coding and OFDM Transmission, Norwegian University of Science and Technology (July 2003), that combines subband coding of the source, for example images, and OFDM modulation.
In digital transmission methods, signals are transmitted in the form of symbols. Each symbol can have one of a predetermined number of possible values. The set of possible values of each symbol is referred to as a constellation and each possible value is referred to as a constellation point. The distance between neighboring points affects the immunity to noise. The noise causes reception of another point instead of the intended point, and thus the symbol may be interpreted incorrectly. In orthogonal frequency division multiplexing (OFDM) communication scheme, the symbols are comprised of multiple bins, e.g., 64, 128 or 256 bins, in the frequency domain, each bin of each symbol comprised of a two dimensional constellation. It is also known in the art that the use of some of the available bins is not recommended. Typically these are the bins located at the ends of the transmission band. Typically, for example in 802.11a/g, some 16 available channels out of the 64, are not used, and hence the efficiency of the band is reduced.
In U.S. patent application serial no, 2004/0196920 and 2004/0196404 by Loheit et al. another scheme is proposed for the transmission of HDTV over a wireless link. The discussed scheme transmits and receives an uncompressed HDTV signal over a wireless RF link which includes a clock that provides a clock signal synchronized to the uncompressed HDTV signal. This scheme also includes a data regeneration module connected to the clock, which provides a stream of regenerated data from the uncompressed HDTV signal. A demultiplexer demultiplexes the stream of regenerated data, using the clock signal, into an I data stream and a Q data stream. A modulator connected to the demultiplexer modulates a carrier with the I data stream and the Q data stream. According to Loheit et al. the RF links operate at a variety of frequency bands from 18 GHz up to 110 GHz, hence requiring sophisticated and more expensive transmitters and receivers.
In view of a variety of limitations of the prior art it would be advantageous to provide a solution that enables the reliable wireless transmission of an HDTV stream while avoiding the need for aggressive or complex compression, or complex hardware implementations. In particular it would be advantageous to avoid a compression that relies on having frame buffers for reaching the compression levels necessary to transmit the vast amount of data required in applications, such as wireless transmission of HDTV data streams. It would be further advantageous to avoid use of ultra-high frequencies to achieve the goal of wireless transmission of an HDTV data stream. It would be of further advantage if the proposed system would not insert delays in the transmission of the video. It would be further advantageous if a more efficient use of the transmission band is achieved, thus allowing the transmission of more information.